The field of the invention is electrical switches, and more specifically, electromagnetically operated switches such as relays and line contactors which have a slidably mounted actuator for effecting engagement and disengagement of one or more sets of contact structures.
Electromagnetic contactors such as that disclosed in U.S. Pat. No. 3,134,869 issued to L. E. Lawrence on May 26, 1964, are commonly employed in motor controls. In such motor controls, the contactor typically includes a set of three main contact structures, or power poles, which are connected to carry three-phase power to the motor. Although three-pole contactors are thus required in the vast majority of installations, it is sometimes necessary to provide additional power poles beyond the three which are normally provided on standard commercially available contactors. For example, in cold climate applications the motor control may operate both a three-phase motor and a space heater which is energized when the motor is stopped. The provision of additional power poles for such an installation has heretofore been treated as a special customer request which required extensive modification of a standard three-pole contactor.
Contactors such as that described in the above-cited U.S. Pat. No. 3,134,869, include an actuator which is slidably mounted to operate the main contacts when an electromagnet is energized. Bias springs associated with the main contacts are compressed during the sliding motion of the actuator to provide contact pressure and the loading on the actuator which results from the bias springs is symmetrically balanced with respect to the actuator axis of motion in order to minimize the frictional wear between the actuator and the guideway in which it slides. Such load balancing must be taken into consideration when additional power poles are added to the contactor.